Investigation of Permeable Asphalt Treated Bases in Alabama
Type of DegreeThesis
MetadataShow full item record
The Alabama Department of Transportation currently uses a permeable asphalt treated base (PATB) course layer consisting of an AASHTO number 57 aggregate gradation with 2.0% to 2.5% asphalt content. The current mixture design employed by ALDOT has been subject of many concerns, namely stability during construction. As a result, the fourth Division has decided to use only polymer modified PG 76 – 22 binder in all of its PATB mixes. An in depth laboratory procedure was devised in order to handle, compact, and test PATB samples, since there was no current procedure available. Field cores and plant mixed PATB were obtained from two different sites within ALDOT’s fourth Division. The cores were tested for air voids, permeability and stability. The plant mix was then compacted to match the field cores in terms of air voids. It was also found that the laboratory produced pills had similar permeability and stability characteristics as the cores obtained from the field. This consequently verified that the procedure outlined to handle, compact, and test PATB samples was suitable. The second phase of the research project investigated alternative mixes for the use of PATB. Number 57 and number 78 gradations consisting of crushed limestone were mixed with 2.0% asphalt. The binder tested consisted of PG 67 – 22 binder and polymer modified 76 – 22 binder. Samples were compacted to a target air void content of 30%. The PATB samples consisting of the number 78 aggregates required less compaction effort than the PATB with number 57 gradation. Furthermore, the PATB with number 78 aggregate had better stability than the PATB with number 57 aggregate and had permeability values above 1,000 ft/day. Based on these results, it is recommended that a field study is performed to determine how PATB consisting of number 78 aggregate performs under traffic and in field conditions.